isir.] GENUS MONOLEPIS. 157 



abrupt, profound fossula for the repose of the abdomen; 

 feet moderate, anterior ones didactyle, second, third, and 

 fourth pairs equal, simple, posterior pair very small, fold- 

 ed on the lateral angles of the thorax, and terminated by 

 elongated setas. 



Abdomen semicylindric, not longer than the thorax, 

 of six segments, first segment very short, concealed by the 

 thorax, second, third, fourth, and fifth equal, consimilar, 

 transverse, convex, with acute posterior lateral angles, 

 sixth segment very short, depressed; natatory feet large, 

 prominent, internal division of the bifid tip, very small; 

 tail as broad at base as the terminal segment of the abdo- 

 men, rounded at tip, simple, concealing the lateral folia- 

 ceous appendages; lateral lamelhs composed each of a 

 single, small, membranaceous, suboval piece, ciliated with 

 long hair, and supported by a short peduncle. 



SPEC IKS. 



1, M. inermis.* Z<2m simple; /zxWyd"^^ very small, 

 terminated by three setae; a large truncate tubercle be- 

 hind each eye; rostrum deflected. 



Inhabits the eastern shore of Maryland. 



Cabinet of the Academy. 



Thorax olivaceous-green, with minute darker spots, 

 an impressed circle between the posterior recipient 

 grooves, two small, geminate, deeply impressed punc- 

 tures, on the middle of the thorax, before which on each 

 side is an obiique, irregular, impressed line; clypeus un- 

 equal, extended into a short rostrum, which is deflected, 

 adpressed to the face, margined, and furnished with a 

 tooth on each side near the eyes; a large truncate tuber- 

 cle behind each eye, upon the lower-edge of the body, as 

 long as the peduncle of the eye; (777i^mory^^^ rather small, 



